1. Field of the Invention
Embodiments presented in this disclosure generally relate to adaptively increasing power delivered to an RF tag.
2. Description of the Related Art
Typical radio frequency identification (RFID) tags or RF tags include a microprocessor functionally connected to an antenna. The microprocessor stores and processes relevant data that may include unique data for identifying a specific item associated with the RF tag. The microprocessor also modulates a radio frequency (RF) signal that is transmitted or backscattered via the antenna. An external tag reader captures the data signal transmitted by the RF tag.
Conventional RF tags are either “active” (with an internal power source for transmitting a modulated signal to the tag reader), “passive” (without any internal power source), or “semi-passive” (includes an internal power source but does not use that power source to backscatter a modulated signal to the tag reader). Passive and semi-passive RF tags are powered by the incident signal transmitted by the tag reader and use that power to backscatter a modulated signal to the tag reader. Passive and semi-passive RF tags are typically less expensive than active tags but have shorter functional ranges than active RF tags.
One limit to the range of the passive and semi-passive RF tags is the power of the transmitted incident signal. At a fixed transmitted power level, the signal attenuates at a certain radius away from the antenna such that the received power at the RF tag is not enough to activate the RF tag's integrated circuit (e.g., microprocessor) that modulates the signal. This limit defines the read zone for the RF tag. Once the RF tag moves beyond the read zone, the RF tag and tag reader can no longer communicate. Moreover, the signal path between the tag reader and RF, tag may be further hindered by multipath fading from destructive interference. Even if the RF tag is within the read zone of the tag reader's antenna, multipath fading may prevent the RF tag from receiving enough power to communicate with the tag reader.